btw: when playing movies using a HTPC and a USB - DAC - is it easy to keep the video and audio in synch or is that something that needs manual delay correction every time?
If its a pain to keep the audio in-synch with the video on a HTPC - then I'm probably better-off going for an A/V processor with HDMI - such as Sherbourn PT-7030 or Onkyo PR-SC5509 - in which case the HDMI-lip-synch-lock is automatic.

The exasound e28 is well beyond my price range... but is perfect and has most of what I want (and some features I don't need) ..

The Twistedpear - Buffalo is something that will need work putting it together and could run more than $600 total

The AKM doesn't look bad - but the performance figures aren't as good as the e28 or Buffalo.

Due to lack of any other viable options... I think I may have to embark on a DIY for the Ultimate multi-channel DAC that would rival the best 2 channel DACs from Antelope and other premium stereo DACs.

Ideally - I'd like to have someone (or a few people) experienced join me in this venture and build this DAC and if sufficient interest is there possibly market and may be even sell this under a direct-internet sales model (like exasound)....

Following are the broad requirement specs:

1. Asynchronous USB input with buffer (no need for SPDIF etc) - optional Ethernet of HDBaseT input in the future.
2. Automatic PCM / DSD Switching (native DSD support)
3. Remote control for power, volume and mode selection
4. Differential DAC output to be maintained through-out analogcircuitry to get 8 channel line level true and fully balanced outputs to gold-plated 3 pin XLR jacks
5. Noise, Crosstalk and Jitter Reduction
6. USB ground isolated galvanically from the DAC and the analogue circuits
7. Digital subsystem powered independently and isolated galvanically from the rest of the board.
8. Like the e28 - does it make sense to have separate Quartz oscillators for (44.1, 88.2, 176.4, and 352.8 kHz) and (48, 96,192 and 384kHz) and another Quartz oscillator as reference master clock with 0.13ps precision for D to A conversion?
9. Need not have internal power transformer - may be we can feed DC power using external laptop-adapter style transformers...
10. Power Cleaning Stages -
11. It would be nice if its a modular design with a single USB digital input and 2ch output and the ability to upgrade by adding expansion 2ch DACs - so as to make 4ch, 6ch, 8ch,10ch or 12ch balanced analog outputs.

Some other considerations:
DAC chip: ESS Technology ES9018 Sabre Reference 32bit (even though its a 8 channel chip - I'd like to use it 4 of these as a stereo DAC for better SNR and Dynamics)
other option is a Texas Instruments - Burr Brown - PCM1794A or DSD1794A or PCM1690?
Any other DAC ships to consider that are 32bit/384kHz or at a minimum 24bit/192kHz or better?

I'd have to say both - because in theory both should be the same - but we all know "sounds ulti" is subjective... whereas "measures ulti" is objective (to an extent, subject to measuring equipment and environment)

therefore what trade-offs/differences/compromises are we talking about when going for either?

A good question. I'd say that for subjective excellence its necessary to pay attention to noise, and noise floor modulation in particular. For objective excellence the attention turns to distortion (THD+N). Subjectively, low-level performance (-30dBfs and below) needs to be optimized because music signals aren't pure sinewaves - rather superpositions of hundreds of small sinewaves. Objectively, the attention goes to performance at full output with a single tone as stimulus.

If you look at how the noise varies for your suggested ES9018 DAC, you can measure something like this. A test tone of around 1kHz is applied, the two colours differ by just 1dB in level but check out the huge shift in the noisefloor. The levels of the two tones are -36dBfs and -35dBfs.

at the end of the day - fidelity is the goal - as in reproducing the studio-recording transparently without extraneous noises or coloring.

i suggested the ES9018 - not out of loyalty or anything but more based on the fact that it seems to have the highest theoretical specs and has been implemented in various high-end brands.

Now to the details:
1. what about the synchronization with video? if this is an issue... an external multichannel Asynchronous USB or Ethernet DAC will only be useful for surround audio and practically meaningless for movies...

2. Can the suggested modular design of a 2Ch DAC with USB input but with ability to add additional 2 DAC baords be achieved? If its tough or too costly this requirement can be dropped.

3. What are the other requirement and design considerations?

4. What would be the estimated parts/material cost (excluding design cost and labor) etc?

Reproducing the studio recording transparently suggests to me you prefer the 'subjective' approach to the objective one. Am I correct?

If I am then the next stage is to ask whether the recording itself has been produced 'transparently' according to the same priorities. And I rather suspect you'll find the answer in many cases is 'no, its produced with equipment designed for the best numbers'. Hence the preponderance of S-D based ADCs in service nowadays with all their noise modulation artifacts which don't show up clearly in the traditional measurements.

__________________ The heart ... first dictates the conclusion, then commands the head to provide the reasoning that will defend it. Anthony de Mello

I somehow knew you were going to talk about the recording equipment itself... lets set that aside for the moment... I'm only concerned about the transparent playback of the lossless audio files that I have (whether it was compressed correctly and without atrificats all that is a different topic) and whether my HTPC/Software (JRiver) etc decoded or uncompressed correctly can also be set aside as outside the scope of our unit...

All we need to focus on is given a set of lossless uncompressed PCM or DSD - our DAC has to stay true to the bits... and give the proper analog rendition of the same...

Rather than get bogged down in discussions over subjective/objective design considerations and parameters - I say let us take our reference product - the exasound e28 or the Buffalo III DAC kit - these are proven and popular and have established a good name ...
Can we follow the same design approach, same parameters/compromises and try to do as good a job or better?

but all this depends on answers on the video-audio-synch issue...
If audio-synch with movies is going to be a routine issue with an external Asynchronous DAC then it would be a true deal breaker for a multichannel DAC whose primary use will be for home-theater movies and not surround audio...

and may be that explains why there aren't that many standalone multichannel DACs marketed for home-theaters - they need HDMI and that means we are talking about more than just a DAC - we are getting closer to the A/V processor territory... in-fact I'm ok with that... we can even consider adding a HDMI input some DSP/decoder chips and a full A/V pass-through HDMI output...

I shall bow out here because I can't get at all excited about aiming at doing a 'better job' (in measurement terms) than a currently available product which is reasonably priced (as it seems to me the exa is).

__________________ The heart ... first dictates the conclusion, then commands the head to provide the reasoning that will defend it. Anthony de Mello

I understand your goal....
and am with you .... but I was getting lost in the "design considerations" debate... ok assuming we are focussing on the ultimate DAC - in which case it has to pass both the Subjective and Objective - Sound quality tests... because the objective is what can be put in to the brochures and the subjective will be left up to the various forum and magazine reviewers and "audio-philes"

and of-course HDMI is not an option - as it would involve exorbitant fees... may be we can consider that as an add-on later if the product does well.

So you'd like this DAC to be a 'crowd sourced' marketed item - from talking about 'brochures' ? If so I doubt you could really sell ultimate SQ in that manner - it would have to be by word of mouth amongst the users. As Krishnamurti said 'Truth cannot be brought down, it has to be ascended to'. 'Ultimate' is not a sales pitch, really.

__________________ The heart ... first dictates the conclusion, then commands the head to provide the reasoning that will defend it. Anthony de Mello